Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/11555#discussion_r55198266
--- Diff:
sql/hive/src/main/scala/org/apache/spark/sql/hive/SQLBuilder.scala ---
@@ -204,11 +208,55 @@ class SQLBuilder(logicalPlan: LogicalPlan,
sqlContext: SQLContext) extends Loggi
private def build(segments: String*): String =
segments.map(_.trim).filter(_.nonEmpty).mkString(" ")
+ private def updateQualifier(
+ expr: Expression,
+ qualifiers: Seq[(String, AttributeSet)]): Expression = {
+ if (qualifiers.isEmpty) {
+ expr
+ } else {
+ expr transform {
+ case a: Attribute =>
+ val index = qualifiers.indexWhere {
+ case (_, inputAttributes) => inputAttributes.contains(a)
+ }
+ if (index == -1) {
+ a
+ } else {
+ a.withQualifiers(qualifiers(index)._1 :: Nil)
+ }
+ }
+ }
+ }
+
+ private def findQualifiers(input: LogicalPlan): Seq[(String,
AttributeSet)] = {
+ val results = mutable.ArrayBuffer.empty[(String, AttributeSet)]
+ val nodes = mutable.Stack(input)
+
+ while (nodes.nonEmpty) {
+ val node = nodes.pop()
+ node match {
+ case SubqueryAlias(alias, child) => results += alias ->
child.outputSet
+ case _ => node.children.foreach(nodes.push)
+ }
+ }
+
+ results.toSeq
+ }
--- End diff --
So this method is basically a DFS search for all the outermost
`SubqueryAlias` operators. Maybe the following version is clearer:
```scala
def findOutermostQualifiers(input: LogicalPlan): Seq[(String,
AttributeSet)] = {
input.collectFirst {
case SubqueryAlias(alias, child) => Seq(alias -> child.outputSet)
case plan => plan.children.flatMap(findOutermostQualifiers)
}.toSeq.flatten
}
```
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